Various types of shoe presses and the like are commonly used for performing pressing operations on a running fibrous web in a paper or board machine. For instance, in the press section of a paper or board machine, the running web is dewatered by pressing the web in one or more shoe presses. Each of the shoe presses comprises a press shoe and a counter roll which between themselves form an extended nip through which the running web is carried by a circulated flexible belt. A plurality of loading cylinders are arranged between a supporting beam of the shoe press and the press shoe and adapted to press the press shoe against the counter roll.
The working chambers in the loading cylinders of some existing shoe presses are pressurized by hydraulic fluid via ducts bored in the frame system of the shoe press. For example, EP 345 501 B2, DE 195 15 832 C1, and DE 44 09 316 C1 each discloses a shoe press in which hydraulic fluid is supplied to the working chambers of the loading cylinders by ducts bored in the frame system. Boring the frame system, in most cases consisting of steel beams, in a shoe press for pressurizing by hydraulic fluid is a complicated and expensive procedure. Furthermore, the bores in the beam cause weakening of the beam, which can allow the beam to be deflected more easily. There is thus a need of simplifying and making the supply of hydraulic fluid to the working chambers of the loading cylinders less expensive, while obviating the other drawbacks mentioned above.
There is frequently also a desire to be able to vary the character of the pressure profile exerted on the running web in the nip of a shoe press, particularly in the machine direction along which the web travels. Accordingly, various mechanisms have been developed for shifting the position of a center of load exerted on a press shoe.
For example, various devices for moving the center of gravity of the supporting force acting on the press shoe relative to the press shoe are disclosed in U.S. Pat. No. 4,713,147, in which a press shoe support between the press shoe and the frame system of the shoe press is movable in the machine direction relative to the press shoe. In a variant, the press shoe support is a hydraulic-fluid-actuatable loading cylinder for pressing the press shoe against the counter roll. The press shoe support is engaged by a set screw journaled in a stationary frame of the shoe press. Rotation of the set screw causes the shoe support to be translated in the machine direction relative to the press shoe. The mechanism is relatively complicated.